There is a need for an inexpensive, compact and energy-efficient motion triggered audio message delivery system to deliver point of purchase advertising to customers in supermarkets, department stores and the like. Preferably, such point of purchase advertising system would be triggered by a prospective customer as he enters into the near vicinity of the product being advertised. It is advantageous that the color of the clothing of the customer not be relevant.
Motion triggered active light beam systems, utilizing an infrared beam directed onto a photosensitive cell which generates a trigger signal when the beam is interrupted by a person moving therethrough, are known. However, this sort of active light beam system is not well adapted for use as a point of purchase advertising system. To catch a potential customer approaching down the supermarket aisle from either direction, two light generating sources must be aligned with two corresponding photosensitive cells located at oblique angles across the aisle. U.S. Pat. No. 4,670,798 to Campbell et al. discloses an active point of purchase advertising system, comprising an ultrasonic sending transducer and an ultrasonic receiving transducer, and a conventional type playback unit, but such type of systems tend to be expensive and power-hungry. U.S. Pat. No. 3,509,288, to Leventhal discloses a passive message delivery system which is triggered by changes in ambient light. However, this system has certain drawbacks. It requires circuitry responsive both to increases in ambient light levels caused by customers wearing relatively bright, light reflecting clothes and decreases in ambient light levels caused by customers wearing relatively dark clothes. Furthermore, it will only detect the presence of a customer who is directly in front of its light sensing device, i.e. it will not detect a customer who is only approaching but not yet in front. Furthermore, this system consumes a lot of power because it uses a conventional electro-mechanic tape playback unit, and requires batteries to be replaced or recharged on a frequent basis.